demo

hint.txt

"Nice try."

main.dart

/// The string concat method with ' ' divider
String stringify(int x, int y) {
}

solution.dart

String stringify(int x, int y) {
  return '$x $y';
}

test.dart

void main() {
  try {
    final str = stringify(2, 3); 

    if (str == '2 3') {
      _result(true);
    } else if (str == '23') {
      _result(false, ['Test failed. It looks like you forgot the space!']);
    } else if (str == null) {
      _result(false, ['Test failed. Did you forget to return a value?']);
    } else {
      _result(false, ['That\'s not quite right. Keep trying!']);
    }
  } catch (e) {
    _result(false, ['Tried calling stringify(2, 3), but received an exception: ${e.runtimeType}']);
  }
}